The present invention relates to a system for self authenticating an item of value, and in particular, to a system for authenticating items by retrieving authenticating data from a storage medium such as a magnetic stripe disposed on the item of value, even if the storage medium has been physically damaged.
Numerous systems have been devised for authenticating articles, particularly those vulnerable to being counterfeited. Examples include imprinting an object with a difficult to copy pattern, application of holographic tape and marking the item with secret identification indicia.
One particularly effective method and apparatus for authenticating articles is described in U.S. Pat. No. 4,423,415, issued Dec. 27, 1983, to Goldman and entitled "Non-Counterfeitable Document System." Although, the Goldman system is effective, additional security may be desired if the item to be authenticated is a high value document such as a stock certificate or bond. One means of increasing security is to encrypt the identifier in a manner such as described in U.S. Pat. No. 4,405,829 entitled "Cryptographic Communications System and Method" issued Sept. 20, 1983, to Rivest et al.
Of specific interest is the method of encrypting using a private key known only to the source, i.e., the entity issuing the stock or bond, but decrypting using a public key known to the public and indeed which may even be identified on the document itself. Successful decryption using the public key will only be possible if the encryption was initially done using the private encryption key. Therefore, successful decryption will indicate the document indeed originated with the stock or bond issuer and is genuine.
Unfortunately, this and other useful encryption techniques result in very large encrypted identifiers which would have to be printed on the document. However, printing such numbers on the document so as to be manually readable is impractical because of the inherent space limitations on the document as well as the difficulty in manually reading such a long number. Therefore, alternative means of storing the anticipated large string of numbers defining the encrypted data on the document are desired.
One means of storing very large quantities of information in a small space is to place a machine readable magnetic stripe on the item itself. However, practical use of a magnetic stripe to store data on a document presently requires that the stripe be printed directly onto the document. Because documents are generally made out of paper and paper has a highly irregular surface contour, a printed magnetic stripe will exhibit a highly irregular geometry which cause wide variations in the magnetic flux characteristic along the length of the stripe. Heretofore, such wide variations in magnetic flux characteristics have resulted in the inability to retrieve data accurately or reliably - an essential requirement when encrypted data is stored to verify authenticity.
Mangetic stripes as well as other storage medium disposed directly onto paper documents such as stock certificates, would in any event be subject to physical damage such as tearing, folding or scratching thereby adding to the difficulty of reliably retrieving data from the document's storage medium. Further exacerbating the problem is the fact that encrypted data must be stored and retrieved without errors. Indeed, any error in reading encrypted data will cause the result of decryption to be "garbage". Therefore, authentication of documents by storing authenticating data on a storage medium disposed directly on the document, particularly where the document must be authenticatable in the presence of possible physical damage, has not heretofore been possible even though use of a storage medium, such as a magnetic stripe, imprinted directly on the document is desired.
Efforts to overcome non-uniform magnetic flux problems so as to enable use of a printed magnetic stripe have included making the magnetic stripe more uniform by improving the method of applying the magnetic composition and by improving the ink formulations. Such efforts have been unsuccessful and, in any event, have not addressed the problem of reliably reading the magnetic stripe in the presence of physical damage.
Another suggested approach has been to attach a strip of magnetic tape over the surface of the document since magnetic tape exhibits uniform magnetic characteristics and can be made strong enough to resist most physical damage. However, overlaying tape on the document is incompatible with current document printing specifications. In any event, application of magnetic tape would make a genuine document vulnerable to damage by removal of the tape.
Therefore, there is a need for an authentication system which includes a document with a storage medium such as a magnetic stripe printed directly on its surface and capable of storing large quantities of data, at least a portion of which data is preferably encrypted, and from which the stored data can be retrieved without errors, even in the presence of physical damage such as tears, folds or scratches, thereby enabling decryption and authenticity verification. The storage medium (stripe) is preferably of the type that is applied by offset printing so as to be highly compatible with the printing of the remaining information on the document of value.